Heather Zichal has advised Obama since his 2008 presidential campaign and took over the role of lead energy advisor after Carol Browner left the White House in 2011. Her departure comes as the president moves to make good on a reinvigorated climate change agenda that he laid out in a speech in June.

“Heather is one of the president’s most trusted policy advisors," White House Chief of Staff Denis McDonough said in a statement announcing Zichal’s departure. "The president values her expertise and counsel and is grateful for her service.”

The statement did not give a reason for Zichal’s departure. Through a spokesman, Zichal declined to comment.

Zichal, the president's deputy assistant for energy and climate change, is expected to leave in the coming weeks. A White House official did not offer any possible replacements. Any successor would have to shepherd controversial initiatives the White House plans to undertake to tackle climate change in the absence of congressional action.

Rules proposed recently by the Environmental Protection Agency to reduce greenhouse gas emissions from new power plants have provoked an outcry from Republicans, business lobbies and politicians from coal states. Rules for existing power plants, certain to be even more contentious, are to be proposed in June 2014.

League of Conservation Voters President Gene Karpinski described Zichal as a “tremendous leader” in the fight against climate change. Zichal played a role in creating tougher fuel efficiency standards, developing mercury and air pollution safeguards and the recent regulations aimed at cutting carbon pollution from power plants, Karpinski said.

“America is better off today because of her commitment to a cleaner, safer world,” Karpinski said.

From the congressional halls to the Jersey shore, here's a look at the best photos surrounding the year's political discourse in 2013. Read more: Debate over the Affordable Care Act. Timeline: Politics in 2013.

WASHINGTON -- After a taking the weekend off, President Obama resumed his public pounding of House Republicans on Monday even as a top aide laid out a possible avenue for defusing the fiscal fight that has frozen parts of the government and threatens a federal default.

WASHINGTON -- The Environmental Protection Agency proposed new rules on Friday to reduce future carbon dioxide emissions from new power plants, a major step to address climate change that industry and some environmentalist say could all but end the construction of coal-fired plants in the United...

A burst of thunderstorm activity across the Chicago area on Sunday afternoon resulted in a death and multiple injuries at an event in west suburban Wood Dale, the collapse of a dome in northwest suburban Rosemont and the temporary evacuation of the music festival Lollapalooza in Grant Park downtown.